1. Field of the Invention
This invention concerns a fuel injected internal combustion engine in which the air intake volume is computed and the amount of fuel injected is based on this computation of the air intake volume.
2. Description of Related Art
It is known to detect the amount of air intake in order to control the amount of fuel injected in fuel injected internal combustion engines. The method used in the past to detect the amount of air intake was to employ an air flow meter, but this increased the air intake resistance and caused changes in the operating characteristics of the engine. More recently, the amount of air intake has been computed using variations in the pressure inside the crank chamber.
An example of the use of computation to determine the air intake volume appears in Japan Patent Hei 2-4785 (1990). In this example, the difference between the crank chamber pressure just prior to the opening of the scavenging port (SPO) and the crank chamber pressure when the scavenging port is closed (SPC) during normal engine operation are used to determine the air intake volume. Alternatively, by way of example, the computation can also be based on detection of the throttle opening and the engine speed.
A problem with the above-described air intake computation methods is that, in marine engines and some other internal combustion engines, external factors such as speed and load changes cause the air intake volume to change compared to the degree to which the throttle is open and the engine speed under other operating conditions. This results in an error between the computed value for air intake volume and the actual volume.
Since the above mentioned prior art fuel injection systems use a computed value for air intake volume as the basis for determining fuel injection, any error between the computed and actual values for the air intake leads to unavoidable degradations in engine performance.